The present invention relates to a shift-assisting device which enables the gear shifting operation to be executed with a decreased force in changing the speed of a transmission mounted on a vehicle.
Large trucks and buses that require a large shifting force for changing the speed have been equipped with a shift-assisting device for executing the shifting operation with a decreased force. The shift-assisting device with which large vehicles are furnished, generally, uses compressed air as a source of operation. The shift-assisting device that uses compressed air as the source of operation, comprises a shift actuator equipped with a pneumatic pressure cylinder that operates the speed-change operation mechanism coupled to a speed-change lever in the same direction as the direction in which the speed-change lever is shifted. Large vehicles generally use compressed air as a source for operating the brake and are, hence, able to use the compressed air for the shift-assisting device. However, small- and medium-size vehicles that are not equipped with a compressor as a source of compressed air, cannot be provided with a shift-assisting device that uses a shift actuator which comprises a pneumatic pressure cylinder. In recent years, however, it has been demanded that even small- and medium-size vehicles be provided with a shift-assisting device, and there have been proposed shift-assisting devices using an electric motor, as disclosed in, for example, Japanese Laid-open Patent Publication (Kokai) No. 87237/1993 and Japanese Patent No. 2987121.
In order to smoothly execute the shifting operation in a shift-assisting device that employs an electric motor, it is desired that the driving force of the electric motor be controlled in response to the operation of the speed-change lever by a driver. According to the shift-assisting devices disclosed in the above Japanese Laid-open Patent Publication (Kokai) No. 87237/1993 and Japanese Patent No. 2987121, a force for operating the speed-change lever is detected, and the driving force of the electric motor is controlled depending on the force of operation. That is, in shifting the transmission equipped with a synchronizing mechanism, the largest operation force is required at the time of accomplishing the synchronizing action in the gear-engaging operation, and next, a fairly large operation force is required for bringing the chamfer of dog teeth into engagement with the chamfer of a spline of a clutch sleeve. In the gear-disengaging operation, further, the operation force is required from the moment of starting the gear-disengaging operation until the dog teeth come out of mesh with the spline of the clutch sleeve. In the shift-assisting device which controls the driving force of the electric motor according to the operation force, however, the electric motor is driven after the operation force has reached a predetermined value, and hence there is a time lag until an assisting force is produced after an increase in the operation force. In executing the shifting operation, therefore, the driver feels a large force just before the electric motor is actuated to produce the assisting force.
It is therefore an object of the present invention to provide a shift-assisting device for a transmission which is capable of leveling the force required for operating the speed-change lever over the whole stroke of the shifting operation.
In order to solve the above-mentioned principal technical assignment according to the present invention, there is provided a shift-assisting device for a transmission having an electric motor for operating a shifting mechanism in the same direction as the direction in which a speed-change lever is shifted, said shifting mechanism being coupled to said speed-change lever to actuate a synchronizing mechanism of the transmission, wherein said shift-assisting device for a transmission comprises:
a shift stroke sensor for detecting a shift stroke position of said shifting mechanism; and
a controller for outputting a control signal corresponding to the shift stroke position to said electric motor based on a signal detected by said shift stroke sensor.
The controller outputs a drive signal to the electric motor over at least a synchronizing range in the shift stroke range of the shifting mechanism at the gear-engaging operation in the shifting operation, and outputs a drive signal to the electric motor over at least a range in which a clutch sleeve of the synchronizing mechanism is in mesh with the dog teeth at the gear-disengaging operation in the shifting operation. Further, the controller sets a driving force of the electric motor in the range in which the clutch sleeve is in mesh with the dog teeth at the gear-disengaging operation to be smaller than a driving force of the electric motor in the synchronizing range at the gear-engaging operation.
The controller, at the gear-engaging operation, outputs a drive signal to the electric motor in at least the synchronizing range in the shift stroke range of the shifting mechanism and in the range in which the chamfer of the clutch sleeve of the synchronizing mechanism is in mesh with the chamfer of the dog teeth. Further, the controller sets a driving force of the electric motor in a range in which the chamfer of the clutch sleeve is in mesh with the chamfer of the dog teeth at the gear-engaging operation to be smaller than a driving force of the electric motor in the synchronizing range at the gear-engaging operation.